638905 has 4 divisors (see below), whose sum is σ = 766692. Its totient is φ = 511120.

The previous prime is 638893. The next prime is 638923. The reversal of 638905 is 509836.

638905 is nontrivially palindromic in base 16.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 137641 + 501264 = 371^2 + 708^2 .

It is not a de Polignac number, because 638905 - 2¹³ = 630713 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 63886 + ... + 63895.

It is an arithmetic number, because the mean of its divisors is an integer number (191673).

2⁶³⁸⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

638905 is a deficient number, since it is larger than the sum of its proper divisors (127787).

638905 is a wasteful number, since it uses less digits than its factorization.

638905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 127786.

The product of its (nonzero) digits is 6480, while the sum is 31.

The square root of 638905 is about 799.3153320186. The cubic root of 638905 is about 86.1282115035.

The spelling of 638905 in words is "six hundred thirty-eight thousand, nine hundred five".